The manufacture of N-alkyl polyhydroxyalkyl amines (N-alkyl polyhydroxy amines), such as N-methylglucamine, has been known for many years, and such materials are available commercially. In the main, however, their use has been somewhat limited and such materials have been relatively expensive. Recently, there has been occasion to employ N-alkyl polyhydroxy amines, e.g., in reactions with fatty acid esters to prepare fatty acid polyhydroxy amide detersive surfactants for use in cleaning products. As can be imagined, were the cost of N-alkyl polyhydroxy amines to remain high, such laundry detergent use of the fatty acid polyhydroxy amide surfactants would be impractical. Accordingly, there is a continuing search for quick, inexpensive means for preparing N-alkyl polyhydroxy amines on a commercial scale.
Moreover, it is has been determined that care must be taken in preparing N-alkyl polyhydroxy amines in a form that is suitable for subsequent reaction with fatty acid methyl esters, since contamination of the N-alkyl polyhydroxy amines with, for example, hydrogenation catalysts such as Raney nickel, unreacted sugars, unreacted amine/sugar adduct, water, and the like, can seriously impact on the formation of the fatty acid polyhydroxy amide formation. For example, browning reactions, with the formation of undesirable color bodies, can occur. The formation of various undesirable by-products such as cyclic materials and/or esteramides can also occur. In a worse case scenario, by-product formation can be so high that the desired reaction of the N-alkyl polyhydroxy amine with the fatty acid methyl ester is essentially stopped in its entirety, with the formation of black, intractable tarry products.
The preparation of N-alkylamino polyols from N-alkylamines, sugars and hydrogen under the influence of nickel catalysis is a known process. However, the resulting N-alkylamino polyol reaction products, such as N-methyl glucamine, are typically contaminated with nickel catalyst and/or contain undesirable odoriferous or colored by-products. Contamination by nickel catalyst or by-products may be tolerable if the user can afford to purify the N-alkylamino polyol prior to use. However, the manufacturer of high volume, low-cost chemicals such as detersive surfactants can ill-afford raw materials which require expensive purification steps. For example, the manufacturer of surfactants which comprise polyhydroxy fatty acid amides (e.g., C.sub.10 -C.sub.12 fatty acid amides of N-methyl glucamine or N-methyl fructamine) requires a source of N-alkylamino polyols which have desirable low color and low odor, as well as low nickel levels. Indeed, the manufacture of high quality polyhydroxy fatty acid amide surfactants relies heavily on having a source of such high quality, yet low-cost, N-alkylamino polyols.
The present invention solves the problem of nickel contamination, odor and undesirable coloration associated with the manufacture of N-alkylamine polyols. It thereby affords access to high quality polyhydroxy fatty acid amide surfactants. Moreover, the catalytic activity of the nickel catalyst used in the present process remains high over multiple reaction sequences, thereby allowing catalyst recycle with attendant, substantial cost savings.
The present invention provides simple means for preparing N-alkyl polyhydroxy amines, especially N-methylglucamine, in high yields, with low color formation, low ionic Ni content, and/or in a form that is particularly suited for, e.g., subsequent reaction with fatty acid esters, or use, either as is, or in quaternized form, as a cation.